Even if things had been going well, Sunday's game against Miami Heat was bound to be a contentious one for Boston Celtics fans. Not only are the hated Heat coming back to town, but they're coming back as defending NBA champions — and they're bringing a turncoat Celtics player, Ray Allen, with them.

To boo, or not to boo?

Ray Allen is no longer a fan favorite in Boston after breaking up with the Celtics to sign with the Miami Heat. Sunday will be his first trip back to Boston in a Heat uniform. (AP Photo)

Allen spent five years in Boston, helping win the 2008 championship, earning a place in the 2010 NBA Finals and surpassing Reggie Miller as the NBA's all-time 3-point king while wearing Celtics green. Though the good memories of Allen remain tangible, it was obvious last year that he had gotten fed up with hearing his name in trade rumors, and chafed at the notion of coming off the bench behind defensive ace Avery Bradley.

When Allen turned down more money to stay with the Celtics and took his talents to Miami, he ticked off former teammates, his former coach and, in turn, a legion of fans in the Northeast.

It seems like ages ago, but remember back on Oct. 30, when the Celtics were in Miami and Kevin Garnett ignored Allen when he went over to shake Garnett's hand as he checked into the game? That kind of frigidity surely awaits Allen in Boston.

"I've thought about it," Allen told reporters. "I think more about who, family-wise, is going, who can go and sorting the whole protocol out. I don't know what to expect from their side. But it's an interesting concept because I've always gotten a warm welcome, even before I started playing there. I just want to win. Everything else will take care of itself."

When he takes the floor on Sunday, he will do so in front of a decidedly conflicted crowd. The Celtics lost out on Allen last summer, but they did bring in Jason Terry, one of the best sixth men going, and solid all-around guard Courtney Lee. With those two behind Bradley, the thinking went, who needs Allen?

Turns out, perhaps it's the Celtics. Terry is averaging 9.8 points, his lowest output since his rookie season, and has shot just 28.6 percent from the 3-point line in his past 12 games. Lee got off to an awful start from the perimeter, and is shooting 33.8 percent on 3s. Bradley is at 33.3 percent and the Celtics as a whole are 27th in 3-point shooting. In three of the five years Allen was in Boston, the Celtics were in the top seven in 3-point shooting.

As for Allen this year, he's shooting 44.3 percent on 3s. What's more, his Heat are on a four-game winning streak and looking to get off to a good start on their four-game road trip with a win on Sunday.

The Celtics, meanwhile, are reeling. Their losing streak was bad enough when it included the likes of the New Orleans Hornets, Detroit Pistons and Cleveland Cavaliers, plus a heartbreaker in overtime to the Chicago Bulls. It grew to five with a hard-fought loss to the New York Knicks on Thursday, but things bottomed out on Friday in Atlanta, when Boston blew a 48-21 lead, and another nine-point lead in the fourth quarter, to lose to the Hawks in double overtime. That made six consecutive losses.

There will be fixation on Allen when Sunday afternoon rolls around, and that is to be expected. But the Celtics find themselves licking their wounds after a crushing come-from-ahead defeat.

When Allen was playing for the Celtics, Miami and Boston measured themselves against each other, the brawniest of East heavyweights. Now, though, the Celtics are 8.5 games behind the Heat.